MD Settings: Lazy-load sub-pages.

chrome/browser/resources/settings/device_page/device_page.html

 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/hardware-icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/image-icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/neon-animatable.html">
 <link rel="import" href="chrome://md-settings/controls/settings_dropdown_menu.html">
 <link rel="import" href="chrome://md-settings/device_page/keyboard.html">
 <link rel="import" href="chrome://md-settings/device_page/touchpad.html">
 <link rel="import" href="chrome://md-settings/i18n_setup.html">
 <link rel="import" href="chrome://md-settings/prefs/prefs.html">
 <link rel="import" href="chrome://md-settings/settings_page/settings_animated_pages.html">
-<link rel="import" href="chrome://md-settings/settings_page/settings_subheader.html">
+<link rel="import" href="chrome://md-settings/settings_page/settings_subpage.html">
 <link rel="import" href="chrome://md-settings/settings_shared_css.html">
 
 <dom-module id="settings-device-page">
   <template>
     <style include="settings-shared"></style>
     <settings-animated-pages id="pages" section="device"
         current-route="{{currentRoute}}">
       <neon-animatable id="main">
         <div id="touchpadRow" class="settings-box first"
             on-tap="onTouchpadTap_">
           <!-- TODO(michaelpg): Get a touchpad icon. -->
           <iron-icon icon="image:brightness-1"></iron-icon>
           <div class="middle">[[i18n('touchpadTitle')]]</div>
         </div>
         <div id="keyboardRow" class="settings-box" on-tap="onKeyboardTap_">
           <iron-icon icon="hardware:keyboard"></iron-icon>
           <div class="middle">[[i18n('keyboardTitle')]]</div>
         </div>
       </neon-animatable>
-      <neon-animatable id="touchpad">
-        <settings-subheader page-title="[[i18n('touchpadTitle')]]">
-        </settings-subheader>
-        <settings-touchpad prefs="{{prefs}}"></settings-touchpad>
-      </neon-animatable>
-      <neon-animatable id="keyboard">
-        <settings-subheader page-title="[[i18n('keyboardTitle')]]">
-        </settings-subheader>
-        <settings-keyboard prefs="{{prefs}}"></settings-keyboard>
-      </neon-animatable>
+      <template is="dom-if" name="touchpad">
+        <settings-subpage page-title="[[i18n('touchpadTitle')]]">
+          <settings-touchpad prefs="{{prefs}}"></settings-touchpad>
+        </settings-subpage>
+      </template>
+      <template is="dom-if" name="keyboard">
+        <settings-subpage page-title="[[i18n('keyboardTitle')]]">
+          <settings-keyboard prefs="{{prefs}}"></settings-keyboard>
+        </settings-subpage>
+      </template>
     </settings-animated-pages>
   </template>
   <script src="device_page.js"></script>
 </dom-module>